Investigating the Effects of Non - Parallel System Irregularity on Seismic Performance of Special Moment-Resisting Steel Frames Using Pushover Analysis

The seismic performance of ۶ steel frames with non-parallel system irregularity has been evaluated in thispaper using pushover analysis. The steel frames were designed based on the ASCE-۷ provisions withdifferent degrees of irregularities. The response modification factors, R, for different structures werepredicted using pushover analysis and the seismic performance of the structures were evaluated andcompared. The effects of increasing the irregularity on the seismic performance of the frames wereinvestigated by evaluating the maximum rotation of the plastic hinges at the target displacement of theframes. The results clearly indicated that as the irregularity increased, the number of the structuralelements exceeding the CP level increased and the overall force modification factor, R, also decreased.The comparison of the inelastic and elastic analysis results indicated that the use of the elastic analysismethods is not appropriate for structures with non-parallel irregularity angles larger than ۲۵ degrees.

Keywords:

Non - parallel system Irregularity , Steel moment resisting frames , Seismic performance , Non - orthogonality of LLRS (Lateral Load resisting systems) , Nonlinear static analysis